Ferrospinel compositions



United States PatentOlice 2,723,239 Patented Nov. 8, 1955 FERROSPINEL COMPOSITIONS Robert L. Harvey,vPrnceton, N. J., assignor to Radio Corporation of America, a corporation oDelaWare Application September29, 1952, Serial No. 312,089

7 Claims. (Cl. 252-,-62.5)

This invention relates to improved ferrospinel compositions, alsofknown as ferrites, and more particularly to improved` ferrospinel compositions having exceptionally small electrical losses.

Previously, many different ferrospinel compositions.

have been developed and described, having diiering advantageous magnetic properties, and some beingfbetter adapted than others to particular uses.

In certain high frequency applications it is desirable to provide a magnetic material having relatively small electrical losses and reasonably high magnetic perme-l ability.

It has now been discovered that the vaddition ofarelatively rsmall amount of C0304 to the mix in the preparationlof a magnesium-zinc-nickel ferrospinel composition provides a final producthaving exceptionally ysmall'electrical vlosses and a satisfactory permeability.

Anobject of the invention is to provide aferrospinel composition having greatly improved electrical characteristics.

Another object of the invention is to provide a ferrospinel composition having exceptionally low electrical loss characteristics together with a reasonably high mag netic permeability.

Another object of the invention is to provide a=ferrospinel composition having properties particularly suitable for use in high frequency applications (0.5 megacycle and upwards) s'uch as, forpexample, loop antennae cores, and high lfrequency inductor and transformer cores.

These and other objects will be more. readily apparent and the invention. more easily understoodby reference to the following detailed description and the drawings, of which;

Figure l showsa curve describing thevalues of theQ ratio' of apparent reactance to apparent resistance in areactive device) obtained in sample bars ofanickelzinc-magnesium ferrospinel composition prepared with the addition of varying amounts of C0304.

Figure 2 is a diagram showing a familyof curvesdescribing the increasevin Q Vobtained by adding 0. l per cent by weight C0304 in the preparation of a large number of dierent 'ferrospinel compositions comprising nickel, zinc, magnesium and iron oxides..

In ferrospinel compositions of the nickel-,zinc and nickel-zinc-magnesium classes, the addition of a relatively minute amount of C0304 provides a core material which in a reactive device provides an improvedvalue vof Q, or decreased electrical losses, and a not excessively diminishedzmagnetic permeability. This" is true o f thosey compositions .containing lessgthan about57 mole percent MgO, andatdeast about 5 mole percent NiO.

In a preferred embodiment-of the invention a mixture!y is intimately mixed together with a quantity of Co304 equal to about.0,1 percentbyweight of the total, and sintered for about one hour, at 9010*.y C. The sintered mixis wet ball milled and then plasticizedby an addition of about 4 percent by weight of a watervenviulsion.y of parafn. The mix is then moldedy by pressing anduiired at 1050" C; for threehours in anon-reducing atmosphere and slow cooled. t

Articles made inthe above described mannerwere tested in a typical reactance deviceV and were foundfto exhibit at Q at 1 megacycley of 320, and an initial permeability (no) of 104. These values may be compared with the corresponding values observed in a molded bodyprepared in exactly like manner as the preferred embodiment but without the addition of C0304. in its preparation, in which casey Q=170 and- )wn- 140. It will be seen that a substantial increase in Q (decrease in electrical losses) has been attained without an excessive lsacrice of permeability.

The same ferrospinel composition may bey preparedv according to thesame proportions of basic ingredients butv with the additionl of dilferent amounts of C0304. By reference tothe curve Vol" Figure 1 it will be seen that a` maximum value of Q (minimum losses) is obtained inl a typicalpreactance device utilizing a magnetic coreV of material according to the instant invention when about 0.1 percent by weight C0304 is added-to the-composition, and that-the addition of C0304 in excess of about 0.1 6 percent by Weight results in no appreciable improvement.

Whilev the curve of Figure 1 describes the variation obtained in electrical losses upon varying the proportion of C0304 added to a particular ferrospinel, Figure `2v describes generally the variations in electrical losses obtained by adding a xed proportion (0.1 percent byy weight) C0304 to difrerent ferrospinel compositions. Some of the materials used in plotting thercurves` of Figure 2 are listed in the table together with their proper-y ties. All measurements from which the data ofv the table and of Figure 2rwere derived were made on toroids having the dimensions of 2.6 cm. outside diameter, 2.2

cm. inside diameter, and 0.2 cm. long. The curves of,

Figure 2,are`,only rough approximations, based to some extent on visual interpolation between points actually.

Upon this system representation have been superimposed curves, each of which shows all compositions found'to exhibit aparticular proportionate increase inthe value of Q upon the addition of 0.1 percent by weight C0304 in their preparation. For example, the curve designated19 has been drawn through all points representing all compositions within the ternary system that exhibit a relative increase in Q of percent upon the addition of 0.1 percent by weight C0304 in their preparation. Since these curves have been drawn based on visual interpolation between known points, the known pointsthemselves have been indicated in order to make clearthe. degree of approximation used in plotting the curves. The specimens listed in the table correspond by number to these points.

5 the reaction product formed by heating an intimate mixture of 0.01 percent to 0.16 percent by weight C0304 and the molar proportions 0.18 NiO, 0.41 ZnO, 0.41 MgO, 0.8 to 1.0 FezOa at 900 C. to 1400 C. for at least one hour under non-reducing conditions.

References Cited in the le of this patent UNITED STATES PATENTS 

1. A COMPOSITION OF MATTER CONSISTING ESSENTIALLY OF THE REACTION PRODUCT FORMED BY HEATING AN INTIMATE MIXTURE OF 0.01 PERCENT TO 0.16 PERCENT BY WEIGHT CO3O4 AND THE MOLAR PROPORTIONS OF 0.15 TO 0.7 ZNO, 0.0 TO 0.5 MGO, 0.05 TO 0.9 NIO, 0.8 TO 1.0 FE2O3 FOR AT LEAST ONE HOUR AT 900* C. TO 1400* C. UNDER NON-REDUCING CONDITIONS. 